Creation: SC 403 appeared in 1933 as a renumbering of SC 301, running from US 76 Timmonsville north to US 401 (now US 15) Lees Crossroads. This is the only SC 403.
Adjustments: In 1942, SC 403 was extended south from Timmonsville after a brief US 76 duplex to end at SC 407 (current S-21-35/83 jct.) at Sparrows.

SC 301 from Timmonsville northward
1932 Official

SC 403 replaces SC 301
1933 Official

SC 403 extended to SC 407
1942 Official

In 1947, SC 403 south was truncated back to US 76 Timmonsville, leaving behind a bit of US 76 and S-21-38 (SC 403 curled northeast on what is now S-21-35 to Sparrows).
In 1968, SC 403 was extended outside Timmonsville with US 76, then replaced SC 53 through Sardis into Sumter County, then replaced all of SC 309 to its current SC 341 endpoint.

SC 403 truncated to Timmonsville
1948 Official

SC 403 replaces SC 53 and SC 309
1969 Official

Between 2006-08, SC 403 north was truncated to SC 34 which is where US 15 was rerouted when the curved piece between SC 34 and SC 403 was removed.
Improvements: SC 403 was paved in 1939 although its 1942-47 extension to Sparrows was not; no multilane segments
Comment: SC 403 is blown off by I-20, which does have a close-by exit with US 401. Otherwise, SC 403 is quiet, serving the small communities of Oats and Sardis, along with an actual town, Timmonsville.